Genome-wide Nucleosome Occupancy Research Articles

Predicting the effect of CRISPR-Cas9-based epigenome editing.

Epigenetic regulation orchestrates mammalian transcription, but functional links between them remain elusive. To tackle this problem, we use epigenomic and transcriptomic data from 13 ENCODE cell types to train machine learning models to predict gene expression from histone post-translational modifications (PTMs), achieving transcriptome-wide correlations of ~ 0.70 - 0.79 for most cell types. Our models recapitulate known associations between histone PTMs and expression patterns, including predicting that acetylation of histone subunit H3 lysine residue 27 (H3K27ac) near the transcription start site (TSS) significantly increases expression levels. To validate this prediction experimentally and investigate how natural vs. engineered deposition of H3K27ac might differentially affect expression, we apply the synthetic dCas9-p300 histone acetyltransferase system to 8 genes in the HEK293T cell line and to 5 genes in the K562 cell line. Further, to facilitate model building, we perform MNase-seq to map genome-wide nucleosome occupancy levels in HEK293T. We observe that our models perform well in accurately ranking relative fold-changes among genes in response to the dCas9-p300 system; however, their ability to rank fold-changes within individual genes is noticeably diminished compared to predicting expression across cell types from their native epigenetic signatures. Our findings highlight the need for more comprehensive genome-scale epigenome editing datasets, better understanding of the actual modifications made by epigenome editing tools, and improved causal models that transfer better from endogenous cellular measurements to perturbation experiments. Together these improvements would facilitate the ability to understand and predictably control the dynamic human epigenome with consequences for human health.

Biased eviction of variant histone H3 nucleosomes triggers biofilm growth in Candida albicans.

Candida albicans lives as a commensal in most healthy humans but can cause superficial skin infections to life-threatening systemic infections. C. albicans also forms biofilms on biotic and abiotic surfaces. Biofilm cells are difficult to treat and highly resistant to antifungals. A specific set of genes is differentially regulated in biofilm cells as compared to free-floating planktonic cells of C. albicans. In this study, we addressed how a variant histone H3VCTG, a previously identified negative regulator of biofilm formation, modulates gene expression changes. By providing compelling evidence, we show that biased eviction of H3VCTG nucleosomes at the promoters of biofilm-relevant genes facilitates the accessibility of both transcription activators and repressors to modulate gene expression. Our study is a comprehensive investigation of genome-wide nucleosome occupancy in both planktonic and biofilm states, which reveals transition to an open chromatin landscape during biofilm mode of growth in C. albicans, a medically relevant pathogen.

CHROMATIN REMODELING 11-dependent nucleosome occupancy affects disease resistance in rice.

Plant immune responses involve transcriptional reprogramming of defense response genes, and chromatin remodeling is important for transcriptional regulation. However, nucleosome dynamics induced by pathogen infection and its association with gene transcription is largely unexplored in plants. Here, we investigated the role of the rice (Oryza sativa) gene CHROMATIN REMODELING 11 (OsCHR11) in nucleosome dynamics and disease resistance. Nucleosome profiling revealed that OsCHR11 is required for the maintaining of genome-wide nucleosome occupancy in rice. Nucleosome occupancy of 14% of the genome was regulated by OsCHR11. Infection of bacterial leaf blight Xoo (Xanthomonas oryzae pv. oryzae) repressed genome-wide nucleosome occupancy, and this process depended on OsCHR11 function. Furthermore, OsCHR11/Xoo-dependent chromatin accessibility correlated with gene transcript induction by Xoo. In addition, accompanied by increased resistance to Xoo, several defense response genes were differentially expressed in oschr11 after Xoo infection. Overall, this study reports the genome-wide effects upon pathogen infection on nucleosome occupancy, its regulation, and its contribution to disease resistance in rice.

Abstract PR14: Sub-nucleosomal fragmentation in urine cell-free DNA

Abstract Cell-free DNA (cfDNA) in plasma has been shown to be a promising analyte for noninvasive diagnostics. The collection of blood plasma requires venipuncture, and plasma volume obtainable at a single point is limited. In contrast, cfDNA in urine can be collected noninvasively, with minimal assistance and in larger volumes. However, so far there has been limited success in diagnostic development using urine cfDNA as urine cfDNA is highly fragmented, and whether the characteristics of these fragments reflect underlying genomic architecture is unknown. Here, we perform a comprehensive characterization of fragmentation patterns in urine cfDNA using high-depth whole-genome sequencing from 30 healthy volunteers. We show the distribution of fragment sizes and genome-wide distribution of urine cfDNA fragments are consistent with transient protection from complete degradation by stable intermediates of nucleosome disassembly. Genome-wide nucleosome occupancy and fragment sizes in urine cfDNA are informative of the cell of origin and renal epithelial cells are among the highest contributors in urine. Based on a reference nucleosome map for urine cfDNA positioning, we developed a computational method to measure the fraction of urine cfDNA fragments with aberrant ends at unexpected genomic loci. We observe a higher fraction of fragments with aberrant ends in pediatric and adult cancer patients, distinguishing cancer samples with an area under the curve of 0.89. Our results demonstrate genomic architecture is preserved to an unexpected degree in urine cfDNA and are proof of principle that genome-wide fragmentation analysis of urine cfDNA can enable cancer diagnostics. This abstract is also being presented as Poster B12. Citation Format: Havell Markus, Jun Zhao, Tania Contente-Cuomo, Elizabeth Raupach, Ahuva Odenheimer-Bergman, Sydney Connor, Bradon McDonald, Elizabeth Hutchins, Marissa McGilvrey, Michelina C. de la Maza, Kendall Van Keuren-Jensen Van Jensen, Patrick Pirrotte Pirrotte, Ajay Goel, Carlos Becerra, Daniel D. Von Hoff, Scott Celinski, Pooja Hingorani, Muhammed Murtaza. Sub-nucleosomal fragmentation in urine cell-free DNA [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr PR14.

LeNup: learning nucleosome positioning from DNA sequences with improved convolutional neural networks.

MotivationNucleosome positioning plays significant roles in proper genome packing and its accessibility to execute transcription regulation. Despite a multitude of nucleosome positioning resources available on line including experimental datasets of genome-wide nucleosome occupancy profiles and computational tools to the analysis on these data, the complex language of eukaryotic Nucleosome positioning remains incompletely understood.ResultsHere, we address this challenge using an approach based on a state-of-the-art machine learning method. We present a novel convolutional neural network (CNN) to understand nucleosome positioning. We combined Inception-like networks with a gating mechanism for the response of multiple patterns and long term association in DNA sequences. We developed the open-source package LeNup based on the CNN to predict nucleosome positioning in Homo sapiens, Caenorhabditis elegans, Drosophila melanogaster as well as Saccharomyces cerevisiae genomes. We trained LeNup on four benchmark datasets. LeNup achieved greater predictive accuracy than previously published methods.Availability and implementationLeNup is freely available as Python and Lua script source code under a BSD style license from https://github.com/biomedBit/LeNup.Supplementary information Supplementary data are available at Bioinformatics online.

A comparison of nucleosome organization in Drosophila cell lines.

Changes in the distribution of nucleosomes along the genome influence chromatin structure and impact gene expression by modulating the accessibility of DNA to transcriptional machinery. However, the role of genome-wide nucleosome positioning in gene expression and in maintaining differentiated cell states remains poorly understood. Drosophila melanogaster cell lines represent distinct tissue types and exhibit cell-type specific gene expression profiles. They thus could provide a useful tool for investigating cell-type specific nucleosome organization of an organism’s genome. To evaluate this possibility, we compared genome-wide nucleosome positioning and occupancy in five different Drosophila tissue-specific cell lines, and in reconstituted chromatin, and then tested for correlations between nucleosome positioning, transcription factor binding motifs, and gene expression. Nucleosomes in all cell lines were positioned in accordance with previously known DNA-nucleosome interactions, with helically repeating A/T di-nucleotide pairs arranged within nucleosomal DNAs and AT-rich pentamers generally excluded from nucleosomal DNA. Nucleosome organization in all cell lines differed markedly from in vitro reconstituted chromatin, with highly expressed genes showing strong nucleosome organization around transcriptional start sites. Importantly, comparative analysis identified genomic regions that exhibited cell line-specific nucleosome enrichment or depletion. Further analysis of these regions identified 91 out of 16,384 possible heptamer sequences that showed differential nucleosomal occupation between cell lines, and 49 of the heptamers matched one or more known transcription factor binding sites. These results demonstrate that there is differential nucleosome positioning between these Drosophila cell lines and therefore identify a system that could be used to investigate the functional significance of differential nucleosomal positioning in cell type specification.

Genome-wide Nucleosome Occupancy and Organization Modulates the Plasticity of Gene Transcriptional Status in Maize

Nucleosomes are fundamental units of chromatin that play critical roles in gene regulation by modulating DNA accessibility. However, their roles in regulating tissue-specific gene transcription are poorly understood. Here, we present genome-wide nucleosome maps of maize shoot and endosperm generated by sequencing the micrococcal nuclease digested nucleosomal DNA. The changes of gene transcriptional status between shoot and endosperm were accompanied by preferential nucleosome loss from the promoters and shifts in the first nucleosome downstream of the transcriptional start sites (+1 nucleosome) and upstream of transcriptional termination sites (−1 nucleosome). Intrinsically DNA-encoded nucleosome organization was largely associated with the capacity of a gene to alter its transcriptional status among different tissues. Compared with tissue-specific genes, constitutively expressed genes showed more pronounced 5′ and 3′ nucleosome-depleted regions as well as further +1 nucleosome to transcriptional start sites and −1 nucleosome to transcriptional termination sites. Moreover, nucleosome organization was more highly correlated with the plasticity of gene transcriptional status than with its expression level when examined using in vivo and predicted nucleosome data. In addition, the translational efficiencies of tissue-specific genes appeared to be greater than those of constitutively expressed genes. Taken together, our results indicate that intrinsically DNA-encoded nucleosome organization is important, beyond its role in regulating gene expression levels, in determining the plasticity of gene transcriptional status.

An integrative analysis of nucleosome occupancy and positioning using diverse sequence dependent properties

Nucleosome organization dictates eukaryotic DNA compaction and access, and plays a critical regulatory role in various eukaryotic genomic functions. It is well known that DNA sequence dependent histone octamer binding is important for nucleosome formation. However, many aspects of the phenomenon remain elusive. Here, we systematically analyze diverse sequence-dependent properties, consisting of multi-scale sequence compositional properties and twelve structural properties on the entire Saccharomyces cerevisiae genome. Based on comparative correlation analysis, the features that are highly correlated with nucleosome formation are identified and are integrated into a multilayer perceptron model for genome-wide nucleosome occupancy prediction. Furthermore, we predict nucleosome positions along genome based on the integrative profile of these properties. The results indicate the substantial effect on nucleosome formation and positioning along the entire genome.

Nucleosome positioning: resources and tools online.

Nucleosome positioning is an important process required for proper genome packing and its accessibility to execute the genetic program in a cell-specific, timely manner. In the recent years hundreds of papers have been devoted to the bioinformatics, physics and biology of nucleosome positioning. The purpose of this review is to cover a practical aspect of this field, namely, to provide a guide to the multitude of nucleosome positioning resources available online. These include almost 300 experimental datasets of genome-wide nucleosome occupancy profiles determined in different cell types and more than 40 computational tools for the analysis of experimental nucleosome positioning data and prediction of intrinsic nucleosome formation probabilities from the DNA sequence. A manually curated, up to date list of these resources will be maintained at http://generegulation.info.

Zelda overcomes the high intrinsic nucleosome barrier at enhancers during Drosophila zygotic genome activation

The Drosophila genome activator Vielfaltig (Vfl), also known as Zelda (Zld), is thought to prime enhancers for activation by patterning transcription factors (TFs). Such priming is accompanied by increased chromatin accessibility, but the mechanisms by which this occurs are poorly understood. Here, we analyze the effect of Zld on genome-wide nucleosome occupancy and binding of the patterning TF Dorsal (Dl). Our results show that early enhancers are characterized by an intrinsically high nucleosome barrier. Zld tackles this nucleosome barrier through local depletion of nucleosomes with the effect being dependent on the number and position of Zld motifs. Without Zld, Dl binding decreases at enhancers and redistributes to open regions devoid of enhancer activity. We propose that Zld primes enhancers by lowering the high nucleosome barrier just enough to assist TFs in accessing their binding motifs and promoting spatially controlled enhancer activation if the right patterning TFs are present. We envision that genome activators in general will utilize this mechanism to activate the zygotic genome in a robust and precise manner.

Genome-Wide Nucleosome Occupancy and Positioning and Their Impact on Gene Expression and Evolution in Plants.

The fundamental unit of chromatin is the nucleosome that consists of a protein octamer composed of the four core histones (Hs; H3, H4, H2A, and H2B) wrapped by 147 bp of DNA. Nucleosome occupancy and positioning have proven to be dynamic and have a critical impact on expression, regulation, and evolution of eukaryotic genes. We developed nucleosome occupancy and positioning data sets using leaf tissue of rice (Oryza sativa) and both leaf and flower tissues of Arabidopsis (Arabidopsis thaliana). We show that model plant and animal species share the fundamental characteristics associated with nucleosome dynamics. Only 12% and 16% of the Arabidopsis and rice genomes, respectively, were occupied by well-positioned nucleosomes. The cores of positioned nucleosomes were enriched with G/C dinucleotides and showed a lower C→T mutation rate than the linker sequences. We discovered that nucleosomes associated with heterochromatic regions were more spaced with longer linkers than those in euchromatic regions in both plant species. Surprisingly, different nucleosome densities were found to be associated with chromatin in leaf and flower tissues in Arabidopsis. We show that deep MNase-seq data sets can be used to map nucleosome occupancy of specific genomic loci and reveal gene expression patterns correlated with chromatin dynamics in plant genomes.

Chromatin mediation of a transcriptional memory effect in yeast.

Previous studies have described a transcriptional “memory effect,” whereby transcript levels of many Abf1-regulated genes in the budding yeast Saccharomyces cerevisiae are undiminished even after Abf1 has dissociated from its regulatory sites. Here we provide additional support for this effect and investigate its molecular basis. We show that the effect is observed in a distinct abf1 ts mutant from that used in earlier studies, demonstrating that it is robust, and use chromatin immunoprecipitation to show that Abf1 association is decreased similarly from memory effect and transcriptionally responsive genes at the restrictive temperature. We also demonstrate that the association of TATA-binding protein and Pol II decreases after the loss of Abf1 binding for transcriptionally responsive genes but not for memory effect genes. Examination of genome-wide nucleosome occupancy data reveals that although transcriptionally responsive genes exhibit increased nucleosome occupancy in abf1 ts yeast, the promoter regions of memory effect targets show no change in abf1 ts mutants, maintaining an open chromatin conformation even after Abf1 eviction. This contrasting behavior reflects different inherent propensity for nucleosome formation between the two classes, driven by the presence of A/T-rich sequences upstream of the Abf1 site in memory effect gene promoters. These sequence-based differences show conservation in closely related fungi and also correlate with different gene expression noise, suggesting a physiological basis for greater access to “memory effect” promoter regions. Thus, our results establish a conserved mechanism underlying a transcriptional memory effect whereby sequences surrounding Abf1 binding sequences affect local nucleosome occupancy following loss of Abf1 binding. Furthermore, these findings demonstrate that sequence-based differences in the propensity for nucleosome occupancy can influence the transcriptional response of genes to an altered regulatory signal.

Stimulation of the Drosophila immune system alters genome-wide nucleosome occupancy.

In eukaryotes, nucleosomes participate in all DNA-templated events by regulating access to the underlying DNA sequence. However, nucleosome dynamics during a genome response have not been well characterized [1], [2]. We stimulated Drosophila S2 cells with heat-killed Gram-negative bacteria Salmonella typhimurium, and mapped genome-wide nucleosome occupancy at high temporal resolution by MNase-seq using Illumina HiSeq 2500. We show widespread nucleosome occupancy change in S2 cells during the immune response, with the significant nucleosomal loss occurring at 4 h after stimulation. Data have been deposited to the Gene Expression Omnibus (GEO) database repository with the dataset identifier GSE64507.

Ubiquitous human ‘master’ origins of replication are encoded in the DNA sequence via a local enrichment in nucleosome excluding energy barriers

As the elementary building block of eukaryotic chromatin, the nucleosome is at the heart of the compromise between the necessity of compacting DNA in the cell nucleus and the required accessibility to regulatory proteins. The recent availability of genome-wide experimental maps of nucleosome positions for many different organisms and cell types has provided an unprecedented opportunity to elucidate to what extent the DNA sequence conditions the primary structure of chromatin and in turn participates in the chromatin-mediated regulation of nuclear functions, such as gene expression and DNA replication. In this study, we use in vivo and in vitro genome-wide nucleosome occupancy data together with the set of nucleosome-free regions (NFRs) predicted by a physical model of nucleosome formation based on sequence-dependent bending properties of the DNA double-helix, to investigate the role of intrinsic nucleosome occupancy in the regulation of the replication spatio-temporal programme in human. We focus our analysis on the so-called replication U/N-domains that were shown to cover about half of the human genome in the germline (skew-N domains) as well as in embryonic stem cells, somatic and HeLa cells (mean replication timing U-domains). The ‘master’ origins of replication (MaOris) that border these megabase-sized U/N-domains were found to be specified by a few hundred kb wide regions that are hyper-sensitive to DNase I cleavage, hypomethylated, and enriched in epigenetic marks involved in transcription regulation, the hallmarks of localized open chromatin structures. Here we show that replication U/N-domain borders that are conserved in all considered cell lines have an environment highly enriched in nucleosome-excluding-energy barriers, suggesting that these ubiquitous MaOris have been selected during evolution. In contrast, MaOris that are cell-type-specific are mainly regulated epigenetically and are no longer favoured by a local abundance of intrinsic NFRs encoded in the DNA sequence. At the smaller few hundred bp scale of gene promoters, CpG-rich promoters of housekeeping genes found nearby ubiquitous MaOris as well as CpG-poor promoters of tissue-specific genes found nearby cell-type-specific MaOris, both correspond to in vivo NFRs that are not coded as nucleosome-excluding-energy barriers. Whereas the former promoters are likely to correspond to high occupancy transcription factor binding regions, the latter are an illustration that gene regulation in human is typically cell-type-specific.

Biophysical Models of Nucleosome Positioning

A human body contains enough DNA to circle the Earth's Equator more than 2.5 million times. The basic units of DNA packaging are called nucleosomes. Their locations along the chromosomes play an essential role in gene regulation. We study nucleosome positioning in yeast, fly and mouse, and build biophysical models in order to explain the genome-wide nucleosome organization. We show that DNA sequence is not the major cause of the regular arrays of nucleosomes observed in vivo near the transcription start sites (TSS). We construct a minimal model in which nucleosomes are positioned by potential barriers located in the gene promoters, and which accurately reproduces the genome-wide nucleosome occupancy patterns observed over the transcribed regions in living cells. Our statistical mechanics model allows us to study nucleosome phasing against potential barriers and wells [1, 2], sequence-dependent nucleosome affinity [2], nucleosome unwrapping [3], competition between different DNA-binding proteins, and accessibility of transcription factors [4, 5] to target sites which are found in nucleosomal DNA, among others. We also discuss alternative nucleosome positioning mechanisms: nucleosome anchoring [6] and active nucleosome positioning by ATP-dependent remodelers [7].[1] RV Chereji, D Tolkunov, G Locke, AV Morozov, Phys. Rev. E 83, 050903 (2011)[2] RV Chereji and AV Morozov, J. Stat. Phys. 144, 379 (2011)[3] RV Chereji and AV Morozov, Proc. Natl. Acad. Sci. U.S.A. 111, 5236 (2014)[4] N Petrenko, RV Chereji, MN McClean, AV Morozov, JR Broach Mol. Biol. Cell 24, 2045 (2013)[5] N Elfving∗, RV Chereji∗, V Bharatula, S Bjorklund, AV Morozov, JR Broach, Nucleic Acids Res. 42, 5468 (2014) (∗ contributed equally)[6] RV Chereji, AV Morozov, YM Moshkin, in preparation[7] D Ganguli∗, RV Chereji∗, J Iben, HA Cole, DJ Clark, Genome Res. (2014) (∗ contributed equally)

Genome-wide nucleosome occupancy and DNA methylation profiling of four human cell lines.

DNA methylation and nucleosome positioning are two key mechanisms that contribute to the epigenetic control of gene expression. During carcinogenesis, the expression of many genes is altered alongside extensive changes in the epigenome, with repressed genes often being associated with local DNA hypermethylation and gain of nucleosomes at their promoters. However the spectrum of alterations that occur at distal regulatory regions has not been extensively studied. To address this we used Nucleosome Occupancy and Methylation sequencing (NOMe-seq) to compare the genome-wide DNA methylation and nucleosome occupancy profiles between normal and cancer cell line models of the breast and prostate. Here we describe the bioinformatic pipeline and methods that we developed for the processing and analysis of the NOMe-seq data published by (Taberlay et al., 2014 [1]) and deposited in the Gene Expression Omnibus with accession GSE57498.

Identifying cooperative transcription factors in yeast using multiple data sources

BackgroundTranscriptional regulation of gene expression is usually accomplished by multiple interactive transcription factors (TFs). Therefore, it is crucial to understand the precise cooperative interactions among TFs. Various kinds of experimental data including ChIP-chip, TF binding site (TFBS), gene expression, TF knockout and protein-protein interaction data have been used to identify cooperative TF pairs in existing methods. The nucleosome occupancy data is not yet used for this research topic despite that several researches have revealed the association between nucleosomes and TFBSs.ResultsIn this study, we developed a novel method to infer the cooperativity between two TFs by integrating the TF-gene documented regulation, TFBS and nucleosome occupancy data. TF-gene documented regulation and TFBS data were used to determine the target genes of a TF, and the genome-wide nucleosome occupancy data was used to assess the nucleosome occupancy on TFBSs. Our method identifies cooperative TF pairs based on two biologically plausible assumptions. If two TFs cooperate, then (i) they should have a significantly higher number of common target genes than random expectation and (ii) their binding sites (in the promoters of their common target genes) should tend to be co-depleted of nucleosomes in order to make these binding sites simultaneously accessible to TF binding. Each TF pair is given a cooperativity score by our method. The higher the score is, the more likely a TF pair has cooperativity. Finally, a list of 27 cooperative TF pairs has been predicted by our method. Among these 27 TF pairs, 19 pairs are also predicted by existing methods. The other 8 pairs are novel cooperative TF pairs predicted by our method. The biological relevance of these 8 novel cooperative TF pairs is justified by the existence of protein-protein interactions and co-annotation in the same MIPS functional categories. Moreover, we adopted three performance indices to compare our predictions with 11 existing methods' predictions. We show that our method performs better than these 11 existing methods in identifying cooperative TF pairs in yeast. Finally, the cooperative TF network constructed from the 27 predicted cooperative TF pairs shows that our method has the power to find cooperative TF pairs of different biological processes.ConclusionOur method is effective in identifying cooperative TF pairs in yeast. Many of our predictions are validated by the literature, and our method outperforms 11 existing methods. We believe that our study will help biologists to understand the mechanisms of transcriptional regulation in eukaryotic cells.

Computational discovery of feature patterns in nucleosomal DNA sequences

The identification of important factors that affect nucleosome formation is critical to clarify nucleosome-forming mechanisms and the role of the nucleosome in gene regulation. Various features reported in the literature led to our hypothesis that multiple features can together contribute to nucleosome formation. Therefore, we compiled 779 features and developed a pattern discovery and scoring algorithm FFN (Finding Features for Nucleosomes) to identify feature patterns that are differentially enriched in nucleosome-forming sequences and nucleosome-depletion sequences. Applying FFN to genome-wide nucleosome occupancy data in yeast and human, we identified statistically significant feature patterns that may influence nucleosome formation, many of which are common to the two species. We found that both sequence and structural features are important in nucleosome occupancy prediction. We discovered that, even for the same feature combinations, variations in feature values may lead to differences in predictive power. We demonstrated that the identified feature patterns could be used to assist nucleosomal sequence prediction.

Nucleosome maps of the human cytomegalovirus genome reveal a temporal switch in chromatin organization linked to a major IE protein

Human CMV (hCMV) establishes lifelong infections in most of us, causing developmental defects in human embryos and life-threatening disease in immunocompromised individuals. During productive infection, the viral >230,000-bp dsDNA genome is expressed widely and in a temporal cascade. The hCMV genome does not carry histones when encapsidated but has been proposed to form nucleosomes after release into the host cell nucleus. Here, we present hCMV genome-wide nucleosome occupancy and nascent transcript maps during infection of permissive human primary cells. We show that nucleosomes occupy nuclear viral DNA in a nonrandom and highly predictable fashion. At early times of infection, nucleosomes associate with the hCMV genome largely according to their intrinsic DNA sequence preferences, indicating that initial nucleosome formation is genetically encoded in the virus. However, as infection proceeds to the late phase, nucleosomes redistribute extensively to establish patterns mostly determined by nongenetic factors. We propose that these factors include key regulators of viral gene expression encoded at the hCMV major immediate-early (IE) locus. Indeed, mutant virus genomes deficient for IE1 expression exhibit globally increased nucleosome loads and reduced nucleosome dynamics compared with WT genomes. The temporal nucleosome occupancy differences between IE1-deficient and WT viruses correlate inversely with changes in the pattern of viral nascent and total transcript accumulation. These results provide a framework of spatial and temporal nucleosome organization across the genome of a major human pathogen and suggest that an hCMV major IE protein governs overall viral chromatin structure and function.

Correction for van der Heijden et al., Sequence-based prediction of single nucleosome positioning and genome-wide nucleosome occupancy

Correction for van der Heijden et al., Sequence-based prediction of single nucleosome positioning and genome-wide nucleosome occupancy